It is well known to deposit aqueous inks, particularly those having dispersed pigment colorants onto a substrate having cations of a multivalent metal salt on the surface thereof. The presence of such multivalent metal cations can be used to prevent deposited ink drops from penetrating too far below the surface of a water-absorptive substrate, thereby preventing a lowering of optical density. The multivalent metal cations can also be used to prevent bleeding or coalescing of adjacent deposited ink drops of the same or different colors on a less absorbent substrate such as a hydrophobic substrate, thereby preventing the formation of blurry or grainy appearing images. Surface treatments comprising aqueous salts of multivalent metal ions are particularly advantageous for high speed printing with page-wide inkjet arrays whereby adjacent drops of ink are deposited within just a few microseconds of each other onto the substrate.
U.S. Pat. No. 9,434,201 (Dannhauser et al.) describes inkjet receiving media suitable for high speed inkjet printing which includes a substrate having a topmost layer coated thereon comprising an aqueous soluble salt of a multivalent metal cation and a cross-linked hydrophilic polymer binder.
U.S. Pat. No. 8,562,126 (Xiang et al.) describes inkjet receiving media comprising a substrate and a topmost layer coated thereon, wherein the topmost layer includes one or more aqueous soluble salts of multivalent metal cations, a cationic polyelectrolyte comprising amidine moieties, and a second polymer which is distinct from the cationic polyelectrolyte comprising amidine moieties. These coatings have improved certain aspects of durability.
Further improvements in durability can be provided using the teaching of U.S. Pat. No. 9,427,975 (Bugner et al.) in which an inkjet printed image is immediately dried after printing, subjected to pure water and heat, and then returned to ambient conditions.
U.S. Pat. No. 9,067,448 (Dannhauser, et al.) describes a topmost layer on inkjet receiving media that includes particles comprised primarily of a waxy polymer and having a Rockwell Hardness of less than R90 and a mode equivalent spherical diameter of at least about 2 micrometers. These particles can be included with the more common aqueous soluble salts of multivalent metal cations. This combination of materials provides more durable media for high speed inkjet printing particularly where the chosen substrates are hydrophobic, such as glossy or semi-glossy coated papers. The resulting inkjet printed images have high image quality, high optical density, and good physical durability (that is, resistance to smearing and wet and dry abrasion).
However, the aqueous substrate “pre-treatment” formulations described in U.S. Pat. No. 9,067,448 (noted above) could be further improved. Some of the particulate waxes described in the publication have a density less than the bulk fluid which forces them to float and to assemble into a coherent structure, making them difficult to re-disperse after standing or particularly during storage. Some of the best particulate waxes such as poly(tetrafluoroethylene) (Teflon) are much denser than the bulk fluid which forces them to settle and pack on the bottom of storage containers, also making them very difficult to re-disperse when the customer is ready to use the aqueous compositions on substrates. It is these problems to which the present invention is addressed.